1. Field of the Invention
The disclosure herein relates generally to the field of obtaining measurements in a subterranean wellbore. More specifically, the present disclosure relates to an apparatus and method for estimating wellbore dimensions.
2. Description of Related Art
An uncased or open hole wellbore diameter can vary along its length. Many devices used for open hole borehole evaluation require accurate knowledge of the wellbore diameter. Additionally, borehole dimension variations can adversely affect data gathering by these devices unless the variations are detected and taken into account during the investigation process. Some currently known open hole interrogation tools capable of evaluating wellbore diameters employ pivoting mechanical arms that extend from the tool up against the wellbore wall. Measuring the arm extension and its pivot angle can be used to determine wellbore diameter.
Other tools include acoustic transmitters that emit an acoustic signal from the tool against the wellbore wall. The signal travels from the transmitter through the wellbore fluid and back to the tool. The signal is received and its travel time to and from the wellbore wall is measured. The tool standoff (distance between the tool housing and wellbore wall) may be calculated based on the measured travel time. The wellbore diameter can then be determined from measured standoff distances and the tool diameter. The amplitude of the reflected acoustic signal will depend on the acoustic impedance contrast between the wellbore fluid and the rock surrounding the borehole, as well as the surface (or geometrical) properties of the borehole wall. Moreover, the acoustic signal may be attenuated by the fluid in the borehole. If the acoustic impedance contrast is small, the reflected signal will be small and may be hard to detect.